Why do birds living near Chernobyl have smaller brains?

Radiation is funny. Not funny ha ha, but rather, funny strange. The health effects of radiation are not at all simple, and in fact, the phrase “health effects of radiation” has a meaning parallel to “the health effects of stuff.” It is vague and refers to many different things. For instance, there are radioisotopes … elements that are “radioactive” because they have unstable nuclei … that do not act like poisons (as arsenic or cyanide or other chemicals might) and those that do. In other words, there are some radioactive elements you can eat and they can sit there in your body and not bother your metabolic systems very much if at all, and others that get involved in your metabolic systems in deadly ways, and still others that are in between. And none of that is really about radiation, but rather, about poison. The “radioactive” part of a radioactive element is about energy and its effects on molecules in your body, and not so much about involvement in metabolic systems.

Metabolic poisons, which includes some radioactive elements but that mostly include other elements, are like agents provocateurs. They insinuate themselves in normal bodily processes, but at some key stage instead of doing what is supposed to be done, they do something very different, everything gets screwed up, and the particular system they were involved in is seriously disrupted and the host organism gets very sick or dies. “Radiation” … such as energy that comes out of radioactive elements … is more like an assassin firing into the body; The energy passes through living tissue like a bullet, and there is a risk of that energy hitting something and breaking it.
Acrocephalus palustris is the old world Marsh Warbler, and is one of the birds in the Chernobyl area. Photo from Wikipedia.

The negative effects occur because a bit of energy interacts with a molecule or fragment of a molecule to disrupt or destroy it. The reason this happens at all is related to the high frequency of the energy. You can (sort of) think of this as how much the energy is spread out. For instance, say you and I are standing in a room and there is an earthquake in the region that causes the room to sway gently about for a moment then everything is fine. Then, I walk over to you and slap you across the face. (So sorry, but this is a necessary part of our thought experiment!) Which of those events actually hurt you? (Answer: The slap.) Which of those events involved more overall energy? (Answer: The earthquake.) Which of those events involved more energy in the room where we were standing (Answer: Still, the earthquake … if I slapped the wall of the room, it would not sway back and forth!) The earthquake energy is spread way out, the slap was very concentrated.

Let’s do another thought experiment. Say I have a machine that puts out energy of any kind, depending on how I set the dial. First, I set the dial to produce the kind of high energy radioactive radiation stuff that would be emitted by an atomic bomb, and calibrate it to dose you (sorry, but this is necessary for our thought experiment!) with 400 rads (a unit of radiation dose) across your whole body. At that rate, you would now have a 50% chance of surviving several days of agonizing “radiation poisoning” in which your tissues would fall apart and all kinds of bad things would happen to you. Alternatively, imagine I set the dial to produce simple heat, like the kind that comes out of your stove to cook your scrambled eggs. I calibrate the machine to produce the same total amount of energy as the previous dose, but instead of being “nuclear bomb” type radiation, it is just stove-type heat.

If I zap you with this heat, you won’t even feel it. If I concentrated the energy on your pinkie, you still won’t feel it. If I concentrate the energy on one heat-detecting neuron in your skin, you might feel it. “Nuclear Radiation” is very high energy type energy …. it is like a slap compared to an earthquake. The vast majority of nuclear rays that hit you from any given source will simply pass right though most of your tissues (depending on the exact kind of energy and the tissue) but if one of these tiny slappy things gets a molecule in your cell, you might end up with broken DNA or some other highly localized but very bad result. The result might be that the cell recognizes itself as messed up and kills itself, or some other cell does it in, or in many cases, the cell will inappropriately produce a chemical that will have a negative effect elsewhere.

This, by the way, is why cell phones won’t give you cancer or radiation poisoning or anything like that. The kind of energy produced by a cell phone signal is way more like the heat that cooks your eggs than like the scary radiation that comes form an H-bomb or X-ray machine or whatever. And, in case you haven’t noticed, if you crack an egg on your cell phone while making a call, all you’ll get is an eggy cell phone, because there is just not enough energy coming out of the thing.

Radiation and Oxidative Stress

The nasty chemical output of a cell being hit by a beam of radiation can be a form of Oxygen or some other chemical that will have an oxidizing effect elsewhere in the body. Messed up Oxygen has to be fixed with the use of various products known as antioxidants. You’ve probably heard of these things, because they are part of a widely known health-kick. Antioxidants are a class of chemicals that interact with oxidants including the reactive oxygen caused by radiation. Both oxidants and antioxidants have various roles in normally functioning cells and tissues, but oxidants can cause undesired changes in important molecules.

So, we need a new analogy. Now, scary radioactive radiation rays are like propaganda from an enemy force. The rays bathe the body and mostly nothing happens, but every now and then one of the rays causes a molecule that was already there to begin to behave badly (as an oxidant) and this molecule now has a potentially negative health effect on the body. At very low doses this is probably meaningless because the badly behaved molecule is dealt with. At very high doses of radiation, oxidants are only one of several problems caused by radiation (like when I killed you with 400 rads, above). But at in between doses, the number of badly behaved molecules that are produced in this manner can matter in subtle but important ways. If there are so many more oxidants floating around, energy must be spent dealing with them instead of being used for growth or maintenance.

The Problem with Brains

And, most interestingly and relevant to the present discussion, tissues that demand lots of Oxygen will have a much higher proportion of oxidants bothering them, because these radiation-induced oxidants will include lots of reactive oxygen. And, of course, of all the tissues that make up a bird or a mammal, neural tissue is the most demanding of oxygen. The brain, then, is the organ most susceptible to the evil propaganda. Radiation exposure will have more of an effect on brains than on other tissues, and possibly a measurable effect, and possibly even an effect that matters to survival.

A recent study, Chernobyl Birds Have Smaller Brains, looks at this in birds at Chernobyl. Corey has mentioned the Chernobyl study before. It is a very nice bit of science. The hypothesis being tested is that high ambient levels of radiation will cause greater production of reactive oxygen in birds, which in turn will stress neural tissue growth processes resulting in smaller brains. Obviously, Chernobyl, the site of the first or second worst nuclear disaster that wasn’t a bomb ever, is a good place to look at this sort of thing.

This study collected data on mean wing length and tail feather length as well as measurements of the head. A separate study conducted within this study showed that the head measurements accurately predicted the brain size in a given bird. So, two body size measurements and one brain size measurement were taken on a sample of birds. In addition, two types of information about radiation were collected: The radiation at the site of data collection was measured with a portable machine, and a map produced by a government survey of the area showing ambient radiation levels was consulted as a check.

The age and sex were also determined for each bird.

The result indicated that only two variables mattered with respect to brain size: Age and ambient radiation levels. Birds living in higher radiation areas had smaller brains if they were one year old. Older birds had more similar brain size.

The brains in the yearlings are not smaller because radiation zapped them and made them smaller, but because growth processes either competed with anti-oxidant processes for energy, or were interrupted or disrupted. This did not happen to other tissues, suggesting that it is the high oxygen demand, and thus the reactive oxygen, that causes the stress on brain development. Birds that are two years old or more seem to not have this problem, meaning, probably, that some birds get ensmallened brains and these birds do not survive. This last bit is something I would not be surprised to see missing in a mammal version of this system; I suspect bird brains are pretty much on the edge regarding energy and size and that mammal brains have a bit more wiggle room. So even if the effect was found in mammals it would be less. However, other brain related problems would likely arise in mammals, and although it is beyond the scope of this post, there have been such reports, at least in humans.

And now, the question you’ve all been asking yourselves; Is the radiation at Fukushima sufficient to cause this to happen there? The answer is yes, at this time, the total amount of ambient radiation in areas around the melted-down Fukushima reactors is about the same or in some cases much more than the range of radiation found during this study at Chernobyl. However, the Chernobyl site has had a lot longer to “cool down.” In other words, in ten years from now, perhaps the area around Fukushima will not be as radioactive as Chernobyl. Also, there is decontamination happening at Fukushima that might be more intensive than what was done at Chernobyl, for various reasons. Finally, a so far unmeasured but seemingly large percentage of the radioactive stuff at Fukushima has been dumped into the ocean rather than spewed into the air. Fish have been shown to have high concentrations of radioactive elements in their bodies in this region. I have no idea if fish really use their brains for much; Fish brains are very small and most fish don’t seem very smart. Perhaps all the Nemos will be turned into Dorys. But I would worry more about fish eating birds along the Fukushima coast.

For the seabirds of this area of Japan, this could be a Tern for the worse.

Greg Laden has been watching birds since they were still dinosaurs, but has remained the consummate amateur. This is probably because he needs better binoculars. Based in the Twin Cities, Minnesota, Greg is a biological anthropologist and Africanist, who writes and teaches about Evolution, especially of humans. He also blogs at Scienceblogs.com. Greg's beat is Bird Evolutionary Biology. One could say that knowing the science of birds can make the birds more interesting. But really, knowing about the birds that go with the science is more likely to make the science more interesting. And thus, birding and Neo Darwinian Theory go hand in hand. Darwin was, after all, a pretty serious birder. Greg has seen a bird eat a monkey in the wild.

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This study has the cause and effect backwards. The correct answer to the title question is, because only birds with smaller brains are dumb enough to live near Chernobyl.

Joking aside, this post is absolutely A+. Thanks for explaining the effects of radiation in a very clear, simple way. I haven’t looked at the study yet, but I was wondering – did they test or only infer that birds with smaller brains had lower survival?